In video encoding methods, it is known to use one of two entropy coding methods in a block-wise prediction coding architecture. One is called context-adaptive binary arithmetic coding (CABAC) and the other one is called context-adaptive variable length coding (CAVLC).
Context modeling provides estimates of conditional probabilities of coding symbols. By utilizing suitable context models, a given inter-symbol redundancy can be exploited by switching between different probability models according to already-coded symbols in the neighborhood of the current symbol to be encoded. Context modeling is responsible for most of CABAC's roughly 10% savings in bit rate over the CAVLC entropy coding method (source: Wikipedia).
Therefore, modern video data coding methods base their efficiency on context-adaptive coding.
In this technical area, there is also known a term of context dilution. As explained in the publication “TOWARDS OPTIMISED CONTEXT SELECTION IN SCALABLE WAVELET BASED VIDEO CODING” (by Toni Zgaljic, Marta Mrak and Ebroul Izquierdo, 15th European Signal Processing Conference (EUSIPCO 2007), Poznan, Poland, Sep. 3-7, 2007), although application of context modeling can significantly improve compression, using too many context models or having too few symbols to be encoded, can result with context dilution, meaning that probability estimations within context model are inefficient since the number of symbols used in each context model is too low to obtain a good probability estimate. In such case data outputted by arithmetic encoder will be expanded. On the other hand, if too few context models are used redundancies between symbols are not efficiently exploited resulting in less efficient compression. Thus, context models have to be carefully selected.
In multiview video coding, context dilution is present with respect to Disoccluded Region Coding (DRC). In DRC there is coded a base view as well as parts of other views (frequently referred to as side views), which became visible due to perspective change with respect to the base view, called disoccluded areas of side views. The disoccluded area in a side view is divided into blocks and coded. Finally, only blocks in the disoccluded areas, are transmitted in an output data stream.
A U.S. Pat. No. 7,817,865 discloses multi-view video data that includes video data of a base view and an ancillary view, the base view indicating a view being decoded independently of other views without using inter-view prediction, the ancillary view being a view other than the base view. If several view sequences to be encoded are given, a center location of the overall arrangement is set to a base view, such that view sequences to be encoded can be hierarchically selected. Images of the reference-view are independently encoded without referring to an image of another view.
Therefore, there is a need to mitigate context dilution during disoccluded region coding, in order to improve compression ratios for side views in multiview coding.